Inorganic Chemistry d-BlockElements

8/9/2019 Inorganic Chemistry d-BlockElements

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Electronic ConfigurationElement Symbol Proton

NumberE. Config

Scandium Sc 21 [Ar] 3d1 4s2

Titanium Ti 22 [Ar] 3d2 4s2

Vanadium V 23 [Ar] 3d3 4s2

Chromium Cr 24 [Ar] 3d5 4s1

Manganese Mn 25 [Ar] 3d5 4s2

Iron Fe 26 [Ar] 3d6 4s2

Cobalt Co 27 [Ar] 3d7 4s2

Nickel Ni 28 [Ar] 3d8 4s2

Copper Cu 29 [Ar] 3d10 4s1

Zinc Zn 30 [Ar] 3d10 4s2

E. c fig f r i a r is t as x ct . [ r]

s a [ r] s c fig rati is rg tically r sta l .


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Transition Element and Their Ions

y Is defined as an element that can form one or more stable

ions with an incompletely filled sub-shell of d-element.

y They are d-block elements but not all elements are

transitional elements.

eg. Scandium and Zinc are not transitional elements

Scandium Sc3+

[Ar] (empty 3d subshell)

Zinc Zn2+

[Ar] 3d10

(full 3d subshell)


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General Physical Propertiesy Hard metal

y Malleable

yHigh heat and electrical conductivity

y Shiny

y High melting points and boiling points

y High densities

yAlmost similar atomic radiiy Low ionisation energies

y Forms colored compounds

y Positive oxidation states


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Variable Oxidation Statesy All transition metals exhibit two or more oxidation states in

their compounds.

y Has a small energy difference between the 3d and 4ssubshells

- atoms can use the outer 4s electrons or theinner 3d electrons for chemical reactions.

- eg. a) Fe: [Ar]3d6 4s2

b) Fe2+: [Ar]3d6 4s0

c) Fe3+ : [Ar]3d5 4s0


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Sc Ti V Cr Mn Fe Co Ni Cu Zn

1

2 2 2 2 2 2 2 2 2

3 3 3 3 3 3 3 3 3

4 4 4 4 4 4 4

5 5 5 5 5

6 6 6

7


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y Maximum oxidation state maximum number of electronsavailable for bonding

y The maximum number of oxidation states increases fromSc to Mn- because all the electrons from the 4s and 3d can be

used for reaction.- eg. Ti(+4) and Mn(+7)

y The maximum number of oxidation states decreases fromMn to Zn- because of the decrease in the number of unpaired

3d electrons.- eg. Ni(+4)


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Cations and Oxo Ions of Transition

Elementsy Transition elements in lower oxidation states (+1, +2,

+3) exist as simple cations.

y However, higher oxidation states (+4 to +7) do notform free aqueous ions- due to their high charge density which will polarise

the water molecules, thus resulting in the formationof oxo-anions.- oxo ions[dichromate(VI), manganate(VII)] usually

have covalent bonds


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y Transition metal ions are good oxidising agents

- eg. Purple manganate(VII) ions and orangedichromate(VI) ion

y The stability of a particular oxidation state may beaffected by the pH of a solution.

- eg. Is stable in alkaline solution butdecomposess rapidly to in acidic solution.


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Oxides of Transition Elementsy Most transition metals react with oxygen to form

oxides.

yThe oxides are nearly all insoluble in water.

y Transition elements with low oxidations states usuallyform basic oxides, whereas those with higher oxidationstates form acidic oxides.

Species Oxidationstate

Properties

+2, +3 Basic

+4 Amphoteric

+7 Acidic


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+2 and +3 Oxidation Statesy All the transition elements from Ti to Cu exhibit both these

two oxidation states in their compounds.y Their relative stability can be predicted based on the

standard electrode potentials.

-compare the standard electrode potential to the oxygensystem below:

System E/V

-0.41

-0.37

-0.24

+0.77

+1.51

+1.81


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y Mn and Co are more stable in the +2 oxidation state

compared to the +3, therefore, and willoxidise water to oxygen:

y However, iron, chromium, vanadium and titanium ismore stable in the +3 oxidation state as oxygen willoxidise :


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Not confined to d-block elements.

Favoured by

High chargeSmall sizeAvailability of empty orbitals.


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Complex Ionsy Involves coordinate / dative bonding.

y Therefore a.k.a. Coordination compounds

y Ligands = Lewis base (electron pair donor)

y Either anion or polar molecule

y Metal ion has empty orbitals in valence shell to

accept lone pair electrons

y Therefore act as Lewis acid.


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Fe3+ + 6CN- [Fe(CN)6]3-

Cu2+ + 4NH3 [Cu(NH3)4]2+

Ni + 4CO- Ni(CO)4


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Al(H2O)63+ (Non transitional)

Aluminium atom 1s22s22p63s23px

1

Aluminium ion 1s22s22p6

3-level orbitals are now empty.

Accept lone pair from SIX water molecules

Why six? Maximum number of water molecules that can fit around aluminium

Maximum no. of bonds = release more energy = energeticallystable

SIX orbitals (3s, three 3p and two 3d) hybridises and produce six neworbitals with the same energy.

Coordination number : 6


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Fe(H2O)63+ (Transition Metal)

Iron atom [Ar] 3s23p63d64s2

Iron(III) ion [Ar] 3s23p63d5

Single electrons in 3d are not used.

4s, 4p and 4d are involved.

Accept lone pair from SIX water molecules

Why six?

Maximum number of water molecules that can fit around iron.

Coordination number : 6


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Type of Ligands

y Monodentate / Unidentate

One donor, one dative bond (with central metal ion)

Like having only one tooth

y Polydentate / Multidentate

One donor, multiple dative bond

More teeth


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Bidentatey Two lone pair which can bond to the central metal

ion.

y Common examples :

y 1,2-diaminoethaney ethanedioate ion

y Visualize chelating effect:

Think of it as a headphone.


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ExamplesyNi (NH2CH2CH2NH2)3

2+

yAbbreviation : [Ni(en)3]2+


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Examplesy Cr (C2O4)3

3-


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Quadridentate

y 4 lone pair eg Haemoglobin

y Iron(II) and haem molecule are involved.

y Haem: Ring of carbon and hydrogen atom with 4

nitrogen at the center. Haem one of the porphyrins.

y Porphyrins are actually an enormous group oforganic compounds

y Eg Chlorophyll

y They have structure like >>>>>>

y Theres two more available spacefor haem


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Haemoglobin

y Protein globin attaches to one of these availablespace.

y Water molecule bonded

can be easily replaced byoxygen (lone pair).

y Carbon monoxide forms

very stable complex and

does not break away again useless haemoglobin


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Hexadentatey 6 lone pair bonded with the same central metal ion.

y Best example : EDTA

y EDTA used as negative ion

y

Entirely wraps up a metal ionusing all 6 position.

y One example is with Cu2+ .

y Drawing the product of this clearly while showing all

the atoms defeats me completely! Here is asimplified version. (Jim Clark)


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Stability of Complex Ionsy Complex ion may undergo ligand substitution.

y More stable is the complex, the more difficult forligand substitution.

y Ligand exchange = equilibrium reactioneg.

y Stability constant :


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Stability of Complex Ions

y The larger the stability constant, the equilibriumfavours forward reaction (to the right).

y Ligand substitution will occur.

y Larger stability constant = product formed is morestable.

y Complex with multidentate ligand are more stable.

y Therefore, EDTA is used in the treatment of heavy

metal poisoning.y Metal ion bounded by EDTA exhibit diminished

reactivity.


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Factors affecting the stability of a complex

(i) Oxidation state of the central metal ion

higher oxidation state,

more stable complex ions.(ii) Type of ligand chelating effect

chelating ligands tend to form more stable complexes thannon-chelating ligands such as water.


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Type of complexesy Cationic complex : [Co(NH3)]3+

yAnionic complex : [CuCl4]2-

y Neutral complex : [Fe(CO)5]


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Nomenclaturey Ligands are named first, then metal without any gap.

y Oxidation state of metal written in Roman numeral

y For neutral and cationic complex, original name ofmetal is used.

y In anionic complex, the suffix ate is added

eg. manganese manganate

y Ligands are named in alphabetical order

yNo. of ligands, use di, tri, tetra, etc

y If di, tri, tetra already exist, use bis, tris, tetrakis, etcand enclosed in a bracket.eg. bis(ethylenediamine)


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Formation of Coloured Ions and Compounds

y In general, why does a transition metal complex appear to

have colour?

It absorbs light at specific wavelengths in visible

regions of electromagnetic spectrum

o Different colours result when certain wavelengths of

light is reflected, transmitted or absorbed after hitting

the substance.

o The reflected light gives the colour of the substance.


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y In an isolated transition metal ion that is not bonded toany other atoms, all five 3dorbital's have the same energy(degeneratedegenerate).

y However in complexes (influence of ligandsinfluence of ligands), the five 3dorbitals are split into two groups with an energy gapbetween them (they are nonthey are non--degeneratedegenerate).

y The energy difference,energy difference, E,E, between the 2 groups of 3dorbital's corresponds to the visible region.

y When the ligands bond with the transition metal ion, thereis repulsion between the electrons in the ligands and theelectrons in the d-orbital's of the metal ion. That raises theraises the

energy of the denergy of the d--orbital's.orbital's.

y However, because of the way the d orbital's are arranged inspace, it doesn't raise all their energies by the sameamount. Instead, it splits them into two groups.splits them into two groups.


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The diagram shows the arrangement of the d electrons in aCu2+ ion before and after six water molecules bond with it.


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Suppose that the energy gap in the d-orbital's of the complex ioncorresponded to the energy of yellow light.

The yellow light would be absorbed because its energy would be used inpromoting the electron. That leaves the other colours.

Your eye would see the light passing through as a dark blue, becauseblue is the complementary colour of yellow.


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y In order for the d-dtransition to occur , ion must havea partially filled dsubshell.

a)Scandium(III) & titanium(IV) complexes are colourless.Sc3+ and Ti4+ ions have emptydsubshells. No d-dtransitionoccurs.

b) Zinc(II) & copper(II) complexes are also colourless. The 3dorbitals are fully filled, no d-dtransition is possible.

c)Metal ions (eg. Na+) have fully filled outer shells. To excitethe electrons to the next available orbital requires highenergy radiation beyond the range of visible light.

Therefore, most ionic group compounds are colourless.


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Factors Affecting the Colour of a Complex Ion

I) Nature of the central metal ion and its oxidationstatesCobalt(II), with ions [Co(H2O)6]

2+ is pink colour

and [CoCl4]2- is blue colour.

Chromium ions, the 2+ ion is pale blue and

the 3+ ion is violet colour.


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II) Nature of ligand

Different ligands have different effects on the energies ofthe d orbital's of the central ion.

y Nh3 is a strong ligand compared to water , gives rise to bigger energygap, E.E.

y Results in a colour change from light blue to dark blue when Nh3 added

to an aq. Sol of a copper (II) salt .


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Coloured Ionsy The characteristics colour are quite useful for simple

transition metal ion identification such as precipitateswith NaOH and Nh3 solutions.

Copper sulphate appears dark blue (left). It is the dipole on

water molecules, that surround the copper ion to form a

complex ion, that disrupts the d-orbital's of copper.


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The anhydrous copper sulfate appears grey in color.

Cobalt chloride(CoCl2.6H2O) appears red.

Nickel sulphate(NiSO4.6H2O) appears green


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Stereochemistry of complex ionsStereochemistry is the study of 3-dimensional structures.

The geometrical shape of a complex ion depends on itscoordination number.

Most common coordination numbers of complexes are 2,4 and 6.

Coordination number Geometrical structure

2 Linear

4 Tetrahedral or squareplanar

6 Octahedral


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Isomerism in complex ions

Stereoisomerism

(i) Geometric isomers

square planar complex (MA2B2)

octahedral complex (MA4B2)

octahedral complex [M(X-X)2B2]

octahedral complex (MA3B3)

* Note : M= central ion

A,B = monodentate ligands

X-X = bidentate ligands


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(ii) Optical isomerism

(I) occurs in octahedral complexes

(ii) mirror image of each other

(iii) optically active and not superimposable

examples: (I)complexes with the formula M(X-X)3(ii) complexes with the formula M(X-X)2B2(iii) complexes with the formula M(EDTA)


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structural isomerism

example : hydrated complex of chromium with the formula [CrCl3(H2O)6]

Isomer Colour Number of moles of AgCl

precipitated

[Cr(H2O)4Cl2 ]+.Cl-.2H2O Dark green 1

[Cr(H2O)5Cl ]2+.2Cl-.H2O Light green 2

[Cr(H2O)6]3+.3Cl- Violet 3


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Uses of transition metals and their

compounds(i) Titanium

Titanium alloys aircraft bodies and space capsules.

Titanium(IV) oxide, TiO2 fillers for plastics and rubber.

Titanium(IV) chloride, TiCl4 Ziegler-Natta catalyst

(ii) Chromium

Chromium metal tan leather.

Dichromate (VI) ion, Cr2O72- strong oxidising agent.

CrO2 ferromagnetic, produce high quality magnetic recording tapes


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(iii) Manganese

Hadfield steel - high speed cutting tools.

KMnO strong oxidising agent

(iv) Iron

man-hole cover

(v) Cobalt

Cobalt (II) chloride test for presence of water

(vi) Nickel

catalyst for turning oils into fats in manufacture of margarine.


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(vii) Copper

electrical wiring

pesticides

(viii) Transitions metal alloys

steel (iron + carbon, other metals) construction of buildings.

(viiii) Transition elements in living system

chromium reducing blood glucose levels.


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Catalytic Properties

Catalyst- substance which alters the rate of chemical reaction but is

not consumed in the reaction.

Some common examples:

Reaction catalyst

Decomposition of hydrogen peroxide manganese(IV) oxide, MnO2

Nitration of benzene concentrated sulphuric acid

Manufacture of ammonia by the Haber

Process

Iron, Fe

Conversion of SO2 into SO3 during the

Contact Process to make sulphuric acidvanadium(V) oxide, V2O5


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y For a reaction to occur, the reacting particles must collide with oneanother.

y Collision with energy equal to or greater than the activation energy willresult in the formation of products.

y A catalyst provides an alternative route for the reaction. Thatalternative route has a lower activation energy.

y Transition elements and their compound are important catalyst:

- exhibit variable oxidation state

- availability ofempty orbitals in their valence shell


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Homogeneous catalysis

Catalyst and reactants are in the same physical stateAbility to change oxidation number

Example:

S2O8 2- + 2I- Fe3+ 2SO42- + I2

The reaction needs a collision between two negative ions

Repulsion


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Stage 1:The iron(III) ions oxidise iodide ions to iodine. In the process, iron(III)

are reduced to iron(II) ions.

2I- + 2Fe3+ I2 + 2Fe2+

Stage 2:The iron(II) ions reduces the persulphate ion to sulphate ions. In the

process the iron(III) ions are regenerated.

S2O82- + 2Fe2+ 2SO4

2- + 2Fe3+

Overall reaction involve collision between positive and negative ions.

This will be much more likely to be successful than collision between two

negative ions in the uncatalysed reaction.


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Heterogeneous catalysis

Catalyst and reactant exist in different physical state.

Has empty orbitals to enable adsorption

Example:

H2 (g) + I2 (g)Ni (s) 2HI (g)

Step 1:

One or more of the reactants are adsorbedon to the surface of

the catalyst


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Step 2:Breaking and formation of bond

- weakening of the covalent bonds in the attached molecules

- new bonds are formed

Step 3:The product molecules are desorbed

-product molecules break away and leaves the active site available for a

new set of molecules to attach to and react.


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Magnetic Properties

Transition metal compounds are:

(Paramagneti en t ey ave ne rmore npaireddelectrons(Weaklyattracted yanexternal magnetic field.

(Diamagnetic whenall electrons are paired.( Not attracted yamagnetic field.

Metals iron, co alt andnickel are:

(

Ferromagnetic(form permenant magnet (remainmagnetizedeven whenmagnetic

field is withdrawn)(attracted to magnets

Inorganic Chemistry d-BlockElements

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